Cathode for electron discharge devices



March 28,1939. N. 'M. RUST ET AL 2,151,803

CATHODE FOR ELECTRON DISCHARGE DEVICES Filed Oct. 21, 1936 INVENTORS NOEL MEYER RUST AND BY GEORGE FAIRBURN BRETT ATTORNEY Patented Mar. 28, 1939 UNITED STATES PATENT OFFICE GATHODE. FOR ELECTRON DISCHARGE DEVICES aware Application October 21, 1936, Serial No. 106,742 In Great Britain November 7, 1935 9 Claims.

Our invention relates to electron discharge devices, more particularly to improvements in cathodes for use in tubes such as disclosed in our co-pending application, Serial No. 678,128 filed June 29, 1933 and assigned to the same assignee as the present application.

The present invention provides detail constructional improvements in a tube including an output electrode constituted by an anode or collector electrode, a cathode, an apertured control electrode for receiving control potentials, e. g. potentials to be amplified and placed relatively close to said cathode and a further apertured electrode which acts as an accelerating anode and is placed relatively close to the last mentioned two electrodes. The arrangement is such that a narrow beam or jet of electrons is projected to the collector electrode. The term electron beam tube is now coming into general use to describe such a tube since the discharge therein is an electron beam or jet (rather than a mere stream) partaking more of the nature of the discharge in a cathode ray tube than of that of the discharge in an ordinary thermionic tube as at present in common use. In use'the accelerating electrode also assists in focussing the electron beam on the collector electrode and by virtue of its position provides a certain amount of screening. In some cases an additional apertured screen or suppressor electrode or electrodes is or are provided adjacent the accelerating electrode and between it and the collector electrode. An electron beam tube may be considered as comprising two main parts or assemblies, an electron gun and a collecting electrode.

The object of the present invention is to provide an improved construction of the gun assembly, more particularly the construction of the cathode and of control electrodes.

In the arrangements specifically described and illustrated in application No. 678,128 referred to, the cathodes are of more or less straight line form and 'are associated with control electrode systems arranged (when viewed from the end of the valve) to surround or partially surround the cathode.

According to the present invention the cathode structure of an electron beam tube is of hollow form and'is arranged to give electron emission from its interior surfaces in the form of a ribbonlike beam of electrons. Preferably the associated control electrode is arranged (when viewed from the end of the valve) more or less within the cathode. One of the principal advantages of this type of modified cathode structure is that a very substantial area of cathode emitting surface may be obtained while still utilizing a gun anode with a relatively small aperture so that minimum capacity between the control and output electrodes is obtained.

The invention is illustrated in the accompanying drawing in which Figures 1 to 4 show one form of cathode and Figures to 7 another form of cathode which may be used in carrying out the invention, and Figures 8 to 11 show schematically four beam tube electrode systems embodying the invention.

In the form of cathode illustrated in Figures 1 to 4 (Figure 1 is a plan view, Figure 2 an elevation, Figure 3 an end view, and Figure 4 a perspective View) the cathode structure consists of two parallel flattened hollow tubes I, 2, oxide coated wholly or partly on the surfaces 3, 4 which face one another. The cathode structure is of such size and shape as to match the aperture in the gun anode. To take a practical example if the gun is a flat element with an aperture mm. mm. then the cathode may be about 10 mm. long (dimension Z) mm. across (dimension w) and about to 1 mm. deep (dimension d)- i. e. about /2 to 1 mm. in the dimension taken parallel to the direction of the electron beam propagation. Such a cathode may be indirectly heated by a suitable heater 5 positioned either outside or (as shown) passing through it. Where a directly heated cathode is desired to be employed it may be made as shown in Figures 5 to 7 (Figure 5 is a plan view, Figure 6 an elevation and Figure 7 a perspective view) in the form of a horse-shoe 6 of flattened strip or metal ribbon. The horse-shoe is provided with oxide coatings or otherwise constructed to give emission from its inner surfaces 3'4.

In the electrode system shown in Figures 8 to l l inclusive C represents the cathode, G the control electrode, A the accelerator anode and P the collector electrode. In all these figures the long axis is at right angles to the plane of the paperi. e. the dimension of the accelerator anode (or other apertured electrode) aperture which appears in any of these figures is the shorter dimension, the cathode in each case appearing in a view corresponding to that of Figure 3 and being represented simply by two vertical lines.

In Figure 8 the control electrode G consists of a wire and in Figure 9 it consists of a strip of metal, the said electrode being placed in each case approximately symmetrically inside the cathode, I

In Figure 10 the control electrode is of flattened cylindrical or tubular form or shaped like the cathode and is placed symmetrically and axially with the cathode between it and the gun anode.

In Figure 11 the control electrode is an apertured plate having an aperture similar in shape to the cathode (when viewed in plan) and placed immediately over it and between it and the anode A. The electrode mount assemblies in Figures 8 to 11 inclusive are mounted within an evacuated envelope E.

While we have indicated the preferred embodiments of our invention of which we are now aware and have also indicated only one specific application for which our invention may be employed, it will be apparent that our invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claims.

What we claim as new is:

1. An electron discharge tube having an envelope enclosing an anode and a cathode, said cathode having a pair of spaced flat oppositely disposed surfaces. facing each other and coated with emitting material only on the facing surfaces for providing a ribbon-like beam of electrons.

2. An electron discharge tube having an envelope enclosing an anode and a cathode, said cathode having a pair of flat parallel elongated members oppositely disposed and having the opposed surfaces facing each other and coated with emitting material only on said facing surfaces for providing a ribbon-like beam of electrons.

3. An electron discharge tube having an envelope containing an anode and a cathode comprising a pair of spaced fiat hollow members oppositely disposed and parallel, the opposed surfaces facing each other and coated with emitting material for providing a ribbon-like beam of electrons, and a heater within said hollow mem- 'bers.

4. An electrondischarge tube having an envelope enclosing an anode and a cathode, said cathode comprising a U-shaped member of strip material, the opposed internal surfaces only of which are coated with emitting material for providing a ribbon-like beam of electrons.

5. An electron discharge tube having an envelope enclosing an anode and a cathode, said cathode having a pair of spaced flat oppositely disposed surfaces facing each other and coated with emitting material only on said facing surfaces which are exposed to each other for providing a ribbon-like beam of electrons, and a control electrode positioned between the flat oppositely disposed surfaces.

6. An electron discharge tube having an envelope containing an anode and a cathode, said cathode having a pair of spaced fiat oppositely disposed surfaces facing each other and coated with emitting material for providing a ribbonlike beam of electrons, and a control electrode positioned at one side of said flat oppositely disposed surfaces and having an aperture registering with the space between the pair of spaced fiat oppositely disposed surfaces, and a second electrode between said control electrode and anode.

7. An electron discharge tube having an envelope enclosing an anode and a cathode, said cathode having a pair of spaced fiat oppositely disposed surfaces facing each other and coated only on the facing surfaces with emitting material for providing a ribbon-like beam of electrons and a pair of electrodes positioned between the cathode and the anode and having openings registering with the space between the flat oppositely disposed surfaces of the cathode.

8. An electron discharge tube having an envelope enclosing an anode, and a cathode comprising a pair of spaced fiat hollow members oppositely disposed and parallel, the opposed surfaces facing each other and being coated with emitting material for providing a ribbon-like beam of electrons, and a pair of electrodes positioned between the cathode and the anode and having openings registering with the space between the fiat oppositely disposed surfaces of the cathode.

9. An electron discharge tube having an envelope enclosing an anode and a cathode, said cathode comprising a U-shaped member of strip material, the opposed facing surfaces only of which are coated with emitting material to provide a ribbon-like beam of electrons, and a pair of electrodes positioned between the cathode and the anode and having openings registering with the space between the opposed surfaces of the cathode.

NOEL MEYER RUST.

GEORGE FAIRBURN BRETT. 

